I installed my taillights from here http://www.webelectricproducts.com/products.htm
I bought the wire it yourself kit but you can also get a premade harness for more $$$ but youcan recoup some if you send them your harness. If you look at "Customer's Cars" you will see more Mustangs than anything.
Mine took about an hour and a half wiring it myself. The brake lights sequence once then go solid. The hazard lights sequence as well. The instructions are great! They also give you extra wire and instructions if you do not want the brake lights to sequence, just ts and hazards. You can do it!

 

this might be a little off topic, but removing the actual light assembly itself is very easy should only take a total of 5 minutes with the correct tools.. anyways... ive had my car almost exactly a year and all four of my damn tailights/break lights have been replaced.... like 9 months in to me having my car i replaced my right middle light.. then right/right goes.. then the left middle goes.. so i just replaced all of them for the heck of it.. i mean the bulbs are only 2 dollars for a pair.. but wtf... has this happened to anyone else.???

 

I have not had a problem gabeh1018.

BTW-when you put the sequencing taillight kit in you car the brake lights light up all three bulbs as it should be. it looks much better IMO.

 

Also check the lights before you button things back up. I put the bulbs back in the order that they came from the factory but the passenger side was out of sequence so I had to swap the sockets around so that they would sequence properly. No biggie but it might save the pain of having to take the cover back off. There was plenty of wire in the factory harness to put the bulbs in order.